The invention relates generally to heat sinks for electronic devices, and more specifically, to dual material heat sink cores for cooling electronic devices.
The use of heat sinks on electronic components is well known. Typically, a heat sink is arranged in close contact with an electronic component, such as a processor chip. Heat generated by the component is transferred to the heat sink and dissipated therefrom. One type of heat sink includes a metallic core in the form of a base plate. Heat dissipating fins extend from the base plate to increase the surface area of the heat sink. Heat transferred from the component to the base plate is spread throughout the base plate and to the fins fixed to the base plate. A fan element circulates air about outer surfaces of the fins and the base to facilitate the transfer of heat from the fins to the air, thereby dissipating heat from the electronic component.
For improved performance, some types of heat sink cores include a cylindrical or rectangular insert or slug in the base plate that is fabricated from a different material (e.g., copper or silver) having a higher thermal conductivity than the base plate, typically fabricated from aluminum. The insert increases the thermal conductivity of the base plate and reduces spreading resistance that inhibits rapid heating of the base plate.
Typically the insert is press fit into an opening in the base plate. The press fit generates elastic forces between the base plate and the insert in a direction parallel to the plane of the opening in the base plate (i.e., a horizontal force). The press fit, however, produces little or no elastic force between the base plate and the insert in a direction perpendicular to the plane of the opening in the base plate (i.e., a vertical force), sometimes referred to as a normal contact force. The amount of normal contact force, however, has been found to substantially affect the performance of the heat sink, especially when the insert is located directly over the heat source. The lack of normal contact force can undesirably result in an air gap being formed between a top surface of the insert and the bottom surface of the base plate. Because the resistance of air is high, heat flow in a vertical direction from the insert to the base plate can be substantially impaired.
In another type of heat sink, the copper or silver inserts are attached to the base plate with a screw, thereby imparting a normal contact force between the insert and the base plate. Inserts attached to a base plate with screws, however, tend to produce little or no contact force between the insert and the base plate in a direction parallel to the base plate. The lack of horizontal contact force reduces heat flow in a horizontal direction between the base plate and the insert, thereby reducing the efficiency of the heat sink. Additionally, to create the desired normal force in these types of heat sinks, the screws are to be located directly over the heat source. Locating the screws directly over the heat source, however, is not always feasible.